Thermoplastic polyurethane (TPU) has been extensively used for producing a variety of medical catheters. Medical catheters, including central venous catheters (CVC), bilumen catheters, trilumer catheters, etc., are commonly used for delivering medicine into the body, or else for drawing blood samples. The inserting end of a medical catheter must be tipped so that it can be conveniently inserted into the body without rendering serious damage to the tissues. Tipping the inserting end is relatively difficult since the outer diameter of regular medical catheters is commonly smaller than 3 mm and its wall thickness is smaller than 0.5 mm. Therefore, proper equipment and a good manufacturing process must be employed for producing medical catheters.
U.S. Pat. No. 4,264,294 of 1981 discloses a conical mold and its processing for the production of medical catheters. U.S. Pat. No. 4,404,159 of 1983 discloses an equipment and process for tipping medical catheters, which is comprised of a movable mold and base for holding the catheter. Wherein, the mold includes a bottom die coupled to an electric heater and a top die coupled to a cooling system. Furthermore the base is comprised of a piston supported on a spring, and a steel needle coupled to the piston. During the tipping process, a catheter is inserted with a steel needle and mounted on the base. Next, the mold is moved to the catheter, thereby permitting the front end of the catheter to be received in the tapered cavity of the mold. The electric heater is turned on to heat the bottom die in order to cause the front end of the catheter to be molded into a tapered tip. Finally, the catheter is removed from the mold and the steel needle after cooling.
U.S. Pat. No. 4,661,300 of 1987 discloses an apparatus and method for tipping medical catheters. The apparatus includes a radio-frequency generator to heat a mold, coolant to cool down the mold and a heated catheter, an infrared sensor to detect the temperature of the mold. During the tipping process, a catheter with a steel needle is mounted on a carriage and moved into the mold by a driving mechanism. The mold is heated by a radio-frequency generator and the front end of the catheter molded into a tapered tip. Next, coolant is applied to the mold to cool down the mold and the catheter. When the temperature of the mold reaches a predetermined value, the catheter is removed from the mold.
U.S. Pat. No. 4,904,433 of 1990 discloses the application of a lubricant to the surface of the catheter so that the catheter can be easily removed from the mold after molding. U.S. Pat. No. 5,102,324 of 1992 discloses the application of AC motor and a belt transmission in a tipping apparatus to move the catheter into the mold.
The aforementioned apparatus and processes are commonly to either move the catheter into the mold for heating and molding or to move the top and bottom dies to the catheter to heat and mold the front end of the catheter into a tapered tip. When the catheter is inserted into the mold during the tipping process, any small error may cause the surface of the catheter to become wrinkled or deformed, and melted material may be left in the mold. Furthermore, the mold needs to be heated first and then cooled down when molding, thereby subsequently resulting in a relatively long production cycle.